The painting shows a woman sleeping in a position that is said to encourage nightmares. She is lying on her back with her head thrown back. An incubus squats on her chest and glares at the viewer while a mare appears between the curtains. The interior is contemporary with the bed and the night table as the only elements that determine the spatio-temporal setting. The architectural aspect is missing and the concept of space is mainly defined by the characters as well as the semblance of movement. This is a closed composition that is centered around the figures that dominate the space which is typical of Fuseli's works.There is a visible contrast between the vertical position of the horse and the incubus and the horizontal position of the young woman which is indicative of the opposition between the evil forces and the victim.

This painting shows the importance of drawing with emphasis on the linear perspective in Fuseli's style to reveal the force and the direction of movement. The line expresses violence and passion, as seen in the contorted and disproportionately elongated body. It is the line that brings motion and rhythm to the composition, in this case, it is both sinewy and tense.

There is a heavy application of the chiaroscuro technique, used to focus the attention on the reclining female figure. It reinforces the dramatic effect and gives an illusion of depth to the different elements of the painting.

The painting is devoid of realism as "nature puts me out," Fuseli said. The painting relied more on his own vision than the study of nature. He therefore paved the way to the use of subjective themes at the end of the 18th century. In contrast to the "noble simplicity" and the "quiet grandeur" advocated by Winckelmann (whose writings Fuseli translated into English as they both shared a passion for antiquity), he was obsessed by all things titanic, grotesque and monstrous, as evidenced by the twisted silhouette of the young woman with a too stretched-out body, revealing the influence of mannerists artists on Fuseli.The clothing molds closely to the woman's body, revealing her figure. It is worth noting that Fuseli dissected cadavers to acquire a good knowledge of muscular and anatomical parts.

As for the incubus and the horse, they look like the bulging-eyed, beastly and demonic characters that come straight from the works of William Blake, Fuseli's contemporary.

At the time, popular folk tales like the Ossian poems were a source of fascination among the Pre-Romantic painters. The subject of nightmares, for example, showed their growing interest in fantasy and the unknown, which set itself apart with the absence of religious and literary symbolisms and whose origins were based on folklore and popular belief.

It is important to analyze the evil characters in the painting.

- The incubus is the creature seated atop the chest of the sleeping woman.

Its name came from the Latin inc- (on top of) and -cubare (to lie), meaning to "lie on top of". Fuseli gave a literal interpretation of the word.

The incubus is a fallen angel characterized by lust, who takes possession of the woman's body during a nightmare, which is likened to sleeping with the devil. The image suggests the occurence of erotic dreams, or of a dangerous and viciously evil form of erotism. Moreover, the incubus manifests itself in the form of Kobold, a German mythological creature.

- The mare is a visual word play on "nightmare". Moreover, in European mythology, the horse is either the demon that causes nightmares, or the animal ridden by this demon.

In French, the word "cauchemar" (for nightmare) is derived from the Picardy term "mare", which is actually borrowed from the Dutch and means nightmare. It refers to a malevolent creature that torments and suffocates people in their sleep, which reminds us of the ghost-like quality of the mare that emerges from the curtains like some kind of apparition.

Fuseli also drew his inspiration from Scandinavian legends, like the Mara, a demon that provokes nightmares, portrayed as a feminine creature who forcefully rides on sleeping folk, like it were a diabolical horseback ride. The Mara sits on the chests of its victims, thereby causing this stifling and heavy sensation. These scenes are established in the painting, brought into view by the mare which represents the ride and the incubus who bears his weight on the woman's torso. Fuseli combined references to these folk legends into one scenario.

Logically speaking, a nightmare arouses feelings of fear and dread that comes from having a terrible and frightful dream.

In the painting, Fuseli showed the physical as well as psychological effects of the nightmare; both the frightening and oppressive situations come into play aside from the symbolic representations.

The Nightmare symbolizes a break in the history of art, since it represents an idea, rather than an event, a myth or a person.

The Nightmare could also mean a reppression of sexual desires, with the incubus as the symbol of the male libido and the horse's intrusion as the symbol of the sexual act. There is a perverse and twisted mind lurking behind this painting, a sadistic form of eroticism which borders between subjugation and aggression with the image of the woman's stiffened body in the throes of hysterical horror.

In 1863, art historian H.W. Janson theorized that nightmares were an expression of unrequited love for Fuseli.

During a trip to Zurich in 1778, Fuseli met the niece of his physiognomist friendLavater--Anna Landholt, with whom the painter fell madly in love but whose father refused to marry her off with him. Shortly after, this failed romance led to a sick obssession over his object of desire.

At the back of the canvas was a portrait of a woman that Janson identified as that of Mlle Landholt. The painting would be a form of persecution--Fuseli addressed his broken heart and crushed hopes, his resentment, jealousy and passion. The painting could be seen as an expression of reppressed desires.

It is interesting to look at this painting from a psychoanalytical perspective although this kind of approach had emerged much later. The Nightmare appears to be one of the first to represent the workings of the unconscious mind, even if the term had not existed during Fuseli's time.

For Freud, dreams are the expression of the unconscious. The nightmare would then be a manner chosen by our unconscious to express a deep and long-forgotten anxiety, or an undisclosable desire, that our unconscious would accept and transform its image into a terrifying nightmare. Nightmares are therefore representations of repressed desires of the self's unconscious.

The Nightmare exemplifies hidden longing, it allows the individual to get acquainted with one's neurosis or to create it. The painting can either represent the repressed desires of Fuseli or those of the sleeping woman. It appears to be a true expression of the shadows, terror and perversion of the mind.

The Nightmare attained great success during its presentation to the Royal Academy in 1782, which led the painter to create several versions, of which a few still exist. The painting would then be copied by caricaturists for satirical purposes during contemporary events. With The Nightmare, Fuseli held on to the belief in the supernatural for some time. As early as 1780 in Europe, the skepticism during the Enlightenment was long gone, giving way to the occult trend.

However, the painter was against this practice. Through his paintings, he showed to the high society that these spirits were only figments of their wild imagination. This would explain the grotesque spirit present in Fuseli's work. Through his figures depicting petrified victims, his Gothic mind, and exploration of the crazy and illogical, Fuseli set the romantic wave in motion.

The subject of dreams and nightmares is an essential element in Fuseli's body of work and would often follow him during the course of his career.

In The Nightmare Leaving Two Sleeping Women (1793), the female is also the victim of demon creatures. The mare can be seen escaping through the window, again reminiscent of the wild horse ride which is often associated with nightmares. This painting is also another expression of Fuseli's repressed desires for the opposite sex, represented by two nude terror-stricken women. For Fuseli, the nightmare is a veritable source of sadistic erotism.

The Nightmare was a source of inspiration to Fuseli's circle of friends. Among them was Abildgaard who created his own nightmare interpretation in 1800. He did not include the mare though he did recapture the incubus sitting on the sleeping woman. It was a more subdued vision, and less violent than Fuseli's.